Summary

• Uric acid is a waste product that is filtered from your blood by your kidneys.
• High levels of uric acid in your blood or urine occur if you are making too much uric acid or if your kidneys are not working well.
• A uric acid test (also called a urate test) is used to help diagnose gout, kidney stones and other health conditions.
• It is also used for monitoring if you are having chemotherapy or radiation treatment for cancer as these can raise uric acid levels.

What is uric acid?

Uric acid is a waste product that your body makes when it breaks down substances called purines. Purines are naturally found in your body’s cells and most of the uric acid in your blood has been released from your cells when they die as part of their natural lifecycle. Purines are also in food, especially sugary drinks, and sweets (due to high amounts of fructose) as well as red meat, liver and kidney meat, certain seafoods and alcohol.

Your kidneys filter your blood, removing waste and water to make urine. The urine flows from your kidneys to your bladder to be disposed of.

As part of this, your kidneys filter uric acid out of your blood. If either you are making too much uric acid or if your kidneys are not working well, uric acid can build up in your body. When this happens, it can form needle-shaped crystals in the fluid around your joints which cause inflammation. This is a common but complex type of arthritis called gout.

Gout usually affects only one or two joints at the same time, typically in the feet and ankles. An attack usually happens at night, causing severe pain and swelling. The pain usually peaks after 12 to 24 hours, then slowly subsides. It often occurs in the big toe, and people can notice it when their bedding rubs on their toe and causes extreme pain. Without treatment, an early attack of gout usually goes away in about a week, and it may be months or years before the next one. As time goes by, more joints can be affected and become chronically swollen.

Gout affects mostly men, and it is very rare in women until after menopause, the time in life when a woman's monthly period stops and especially if they are taking diuretics. Gout in young women is extremely rare and needs special investigation.

Uric acid test

When uric acid dissolves in body fluids, it forms urate. Uric acid and urate are two forms of the same substance and most of the uric acid exists as urate.

The test measures the amount of urate in a sample of your blood or urine to find out whether your body might be breaking down cells too quickly or not removing uric acid quickly enough due to poor kidney function.

Why get tested?

Gout

A uric acid blood test is used to help diagnose gout. However, uric acid testing is not enough to diagnose gout by itself, and test results should be interpreted along with other clinical findings. Many people with high blood levels of uric acid never develop gout, and some people with an acute gout attack may have normal levels since uric acid levels can fluctuate.

The definitive diagnosis of gout is made by collecting some fluid from an affected joint and looking for urate crystals. This can confirm the presence of crystals, which are the cause of gout. The uric acid test can also be used to monitor the risk of developing kidney stones if you have gout.

Other conditions

Uric acid levels are measured if you are having cancer chemotherapy or radiation therapy. These treatments work by killing cells with the result that more purines are released into the blood.

Uric acid levels can also rise in pre-eclampsia and are sometimes measured during pregnancy.

In general, testing a blood sample is preferred to using a urine sample because it is both a very accurate test and more convenient for the person having the test. However, a 24-hour urine collection might be requested:

• When investigating whether high uric acid levels are due to too much being made or not enough being removed by the kidneys.
• For investigating uric acid kidney stones.
• To clarify ambiguous cases where high uric acid blood levels do not clearly explain clinical symptoms.

Having the test

Sample

Blood or urine.

Any preparation?

None

Your results

Reading your test report

Your results will be presented along with those of your other tests on the same form. You will see separate columns or lines for each of these tests.

Interpreting your results

High uric acid

Higher than normal uric acid levels mean that your body is not handling the breakdown of purines well. Your medical team will have to find out whether the cause is over-production of uric acid, increased intake of purine-rich food, or if your body is unable to remove the uric acid because your kidneys are not working properly.

Uric acid levels can vary throughout day and from week to week. For this reason, there is some discussion about what the “normal” level is for a uric acid test. Your doctors may request several uric acid tests over a period of time to get a clearer idea of your levels.

Depending on the condition that causes your high uric acid levels, you may not need to take medication. For some people lifestyle changes are all that is needed with weight loss, if required, and a change in eating habits by moving to a healthier diet.

If you have a sudden spike in uric acid level, as with an attack of gout, your doctors may treat you with colchicine and a nonsteroidal anti-inflammatory drug, such as aspirin or ibuprofen. This treatment is usually short term. However, you may have to stay on a maintenance therapy for a while until your uric acid levels come under control. You may be given drugs such as probenecid that help to clear your system of uric acid salts or you may be given drugs such as allopurinol that interfere with uric acid production.

If you have high uric acid levels because of chemotherapy or radiation, you may have to have uric acid tests more often and have treatment. A medication called rasburicase may be used for this.

Low uric acid

Low uric acid levels are not as common as high levels. Low uric acid levels can be due to:

• A rare deficiency of an enzyme that makes uric acid.
• Severe liver disease.
• An issue with your kidneys where it is filtering out too much uric acid.
• Some medications that reduce uric acid levels.
• A diet that is unusually low in purines, but this is uncommon.

Reference intervals

Your results will be compared to reference intervals (sometimes called a normal range).

• Reference intervals are the range of results expected in healthy people.
• When compared against them your results may be flagged high or low if they sit outside this range.
• Many reference intervals vary between labs so only those that are standardised or harmonised across most laboratories are given on this website.

If your results are flagged as high or low this does not necessarily mean that anything is wrong. Your doctor needs to take your medical history to help interpret your result.

Any more to know?

Many medications can increase or decrease the level of uric acid. Aspirin (and other salicylates) have varying effects on uric acid. At low aspirin levels (as may occur in people taking aspirin only occasionally), aspirin can increase blood uric acid. On the other hand, when taken in high doses (as may be used to treat rheumatoid arthritis), aspirin actually lowers the concentration of uric acid.

Questions to ask your doctor

The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.

You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.

Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements. These may affect your results. Ask:

• Why does this test need to be done?
• Do I need to prepare (such as fast or avoid medications) for the sample collection?
• Will an abnormal result mean I need further tests?
• How could it change the course of my care?
• What will happen next, after the test?

More information

Pathology and diagnostic imaging reports can be added to your My Health Record. You and your healthcare provider can now access your results whenever and wherever needed.

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